Which domestic abusers will go on to commit murder? This one act offers a clue.

Carrie Matula embraces a woman after a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Sunday, Nov. 5, 2017. Matula said she heard the shooting from the gas station where she works a block away. (Nick Wagner/Austin American-Statesman via AP)

Flowers and stuffed animals rest at the base of crosses at a makeshift memorial for the First Baptist Church victims Tuesday, Nov. 7, 2017, in Sutherland Springs, Texas. A man opened fire inside the church in the small South Texas community on Sunday, killing more than two dozen and injuring others. (AP Photo/David J. Phillip)

In 2012, while stationed at Holloman Air Force Base in New Mexico, Devin Patrick Kelley assaulted his wife and stepson. Kelley was subsequently convicted of domestic violence and released early from the Air Force.

One important detail of the attack: In addition to fracturing the child’s skull and hitting and kicking his wife, Kelley strangled her. If the particular severity of his violence had been better understood and recognized in New Mexico, 26 people, including a 17-month-old baby named Noah, might not have been killed in Sutherland Springs, Texas, this month. (Continued below)

Strangulation inhabits a category all its own in domestic violence as a marker of lethality. A kick, a punch, a slap, a bite - none of these, though terrible, portend homicide like strangulation does. And while the link between mass shooters and domestic violence is increasingly recognized in the public arena, articles and op-eds, strangulation as a specific sign of lethality in the context of domestic violence remains largely unknown.

The U.S. Sentencing Commission recognized strangulation as a marker of dangerousness in a 2014 report and recommended increased prison time - up to 10 years - for those convicted of it. Indeed, 45 states now recognize strangulation as a felony. New Mexico, where Kelley was convicted, is not one of them.

Kelley, as we know now, served just one year for the assault on his wife and stepchild, after which he was discharged from the Air Force for “bad conduct.”

Bad conduct is going 80 in a 55 mph zone. Bad conduct is cutting down your neighbor’s azaleas or flirting with your colleague’s wife. Bad conduct is not engaging in an act so violent that it could take the life of another human being.

Omar Mateen, the Orlando Pulse nightclub shooter, had also choked both his wives and was never charged, let alone prosecuted. He and Kelley should not have had access to guns, true enough, but more to the point, they should have been behind bars.

The list goes on. Take Cedric Ford, who in 2016 fatally shot three of his co-workers and injured 14 others in Kansas, but prior to that was charged only with misdemeanor domestic violence for choking his ex. Then there’s Esteban Santiago. He killed five and injured six in a shooting at the Fort Lauderdale Airport early this year. He, too, had been charged with a misdemeanor after strangling his ex. (Kevin Neal, who killed his wife and four other people in Northern California this week, had a history of domestic violence, though it’s not clear if that included strangulation.)

Gael Strack, chief executive of the Training Institute on Strangulation Prevention in San Diego, says the mere presence of strangulation in a situation of domestic abuse increases the chances of homicide sevenfold. It is a clear trajectory from escalating violence to homicide, of which strangulation is the penultimate act. “Statistically, we know that once the hands are on the neck, the very next step is homicide,” Strack said. “They don’t go backwards.”

Casey Gwinn, president of the Alliance for Hope International and a co-founder of the Training Institute for Strangulation Prevention along with Strack, wrote in an email to me that Kelley “was a rage-filled domestic violence strangler and child abuser who had left every possible lethality marker for a mass shooter we know of in plain sight.”

Yet strangulation, as a signal of dangerousness, is not only overlooked by most law enforcement officers and prosecutors, it’s not always recognized by health-care workers.

Symptoms can appear days or months afterward. Victims are regularly released from emergency rooms without undergoing CT scans or MRIs. Most strangulation injuries are not visible enough to photograph, and police often don’t know to look for other signs - including urination, slurred speech, redness around the eyes or scalp, a hoarse voice, or trouble swallowing. As a result, injuries are played down in police reports and commonly noted as mere scratches or redness around the neck, according to a study by Strack of 300 nonfatal strangulation cases. Many victims have poor recall of events - often a result of loss of consciousness from the strangulation. In fact, a person can be strangled in less than 12 seconds and never stop breathing.

It wasn’t that Kelley operated under the radar; it was that authorities failed to see and then act on the clues he was leaving.

So, while we’re offering up theories as to Kelley’s motives - he was an atheist, he was a liberal, he was mentally ill, he was a loner, he was a weirdo - we can also consider this single fact: He was a strangler.

He was a strangler whose violent act was described as “choking” in the report on his 2012 assault. Law enforcement officers may not have known about strangulation as a marker of dangerousness the night they were called to his home. Or they may not have known how to look for the signs of strangulation. Perhaps they had never been trained. Perhaps they dismissed the call as just another “domestic” in a long string of frustrating domestics. Whatever happened that night, because Kelley was not charged with nonfatal strangulation as a felony, he was not prosecuted accordingly. And because he was not prosecuted accordingly, he was not sentenced to the 10 years he could and should have gotten in prison, where he would remain today. And because he was not in prison, he was out in the world with the rest of us: a dangerous man, legally free and simmering.

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Snyder is an associate professor at American University and author of the forthcoming book “No Visible Bruises: How What We Don’t Know About Violence Can Kill Us.”